1. Field of the Invention
The present invention relates generally to methods and devices for managing the liquid and gaseous components of a variable pressure stream. More particularly, embodiments of the present invention relate to an exhaust emissions separator for management of internal combustion engine exhaust components.
2. Prior State of the Art
The popularity and widespread use of two-stroke engines is undisputed. Such engines are in extensive use throughout the United States, as well as in both industrialized and developing nations around the world. In particular, two-stroke engines are the power source of choice in such varied applications as snowmobiles, outboard motors, all-terrain vehicles, off-road vehicles, scooters, mopeds, lawn mowers, and chain saws, to name but a few. The typical two-stroke engine possesses a variety of features which make it ideally suited for such applications.
One such feature is the relative simplicity of the two-stroke engine. In general, the two-stroke engine possesses relatively few moving parts and components as compared to, for example, the more complex four stroke engine, so that operation and maintenance of the two-stroke engine is relatively simple. Further, because of this simplicity, a two-stroke engine is less likely to experience the breakdowns and failures that characterize more complex engines, and is thus somewhat more reliable. Another consequence of the relative simplicity of the two-stroke engine is that because the two-stroke engine utilizes relatively few parts, it can be readily produced at relatively low cost.
The simplicity of the two-stroke engine has other important consequences as well. For example, because of the relatively few parts employed in typical two-stroke engine designs, the two-stroke engine can be made very compact and light in weight. As a direct result of its light weight, the typical two-stroke engine has a relatively high power to weight ratio (PWR). The relatively high PWR of the typical two-stroke engine makes it ideally suited for applications, such as those noted above, where a relatively large amount of power is required, but where excessive engine weight would likely compromise the overall performance of the device.
While two-stroke engines possess numerous advantages, such engines are not without their shortcomings. A major shortcoming of typical two-stroke engines is their propensity to discharge exhaust containing a relatively large amount of unburned fuel and/or oil. This characteristic is primarily a consequence of the construction of the engine. In general, two-stroke engines operate in such a way that the vacuum created in the combustion chamber by the exit of pressurized exhaust serves to pull a fresh volume of unburned fuel and oil into the combustion chamber, preparatory to the compression stroke. As a result of the substantially simultaneous exit of exhaust and entry of unburned fuel, some of the unburned fuel and/or oil are pulled from the combustion chamber along with the exhaust, and discharged, unburned, to the atmosphere.
The omission of unburned oil and gas from the two-stroke engine exhaust is problematic for a number of reasons. First, any unburned gas omitted is necessarily gas that is not available for operation of the engine. Thus, the operational efficiency of the engine with regard to a given amount of fuel is significantly compromised. In fact, it is estimated that as much a twenty five percent to thirty five percent of the fuel that enters a typical two-stroke engine exits unburned with the exhaust. Thus, while they possess other significant advantages, two-stroke engines are not particularly fuel-efficient.
While the emission of unburned fuel, oil, and other heavy hydrocarbons, is of some interest insofar as the fuel efficiency of two-stroke engines is concerned, another significant effect of such emissions is the severe impact that they have on the environment. For example, the discharge of raw engine oil and fuel from outboard engines is a major cause of pollution in both fresh-water and salt-water waterways. It is estimated that nearly 166,000,000 gallons of petroleum products are discharged into the waterways of the United States alone each year. This high volume of pollutants is a direct consequence of the ubiquity of two-stroke engines and their operational characteristics.
Pollution generated by outboard engines, jet skis, and other water-based platforms is not limited solely to waterways however. At least some of the unburned fuel, oil, and heavy hydrocarbons are emitted as vapor from the engine. Thus, the two-stroke engines typically employed in water-based platforms pollute the air as well as the water. Pollution of the air is further exacerbated by land-based two-stroke engine platforms such as snowmobiles, chain saws, weed trimmers, motorcycles, and the like. Air pollution resulting from two-stroke engines is particularly problematic in developing nations where the two-stroke engine is widely used in personal transportation applications. Finally, these land-based platforms also pollute the soil, and consequently the groundwater, when they discharge oil and fuel onto the ground. The negative impacts of such pollution on the environment as well as humans and animals are well-documented. Consequences associated with such pollution include, but are not limited to, respiratory distress, aquatic toxicity and mutagenicity.
The multitude of problems induced by the operation of two-stroke engines has not gone unnoticed. The manufacturers and users of such engines have come under substantial pressure, from regulatory agencies, environmental groups, and the like to severely restrict, if not cease all together, the manufacture and/or use of two-stroke engines. For example, the use of such engines has been banned in at least some national parks. Further, it appears that actions such as use bans and the like are likely to become increasingly commonplace as the protest against the use of two-stroke engines gains momentum.
In response to such pressures, and in an effort to preserve the viability of two-stroke engine based applications, industry has made a number of attempts to resolve the pollution problems inherent in two-stroke engines. As discussed below however, unacceptable costs and/or drawbacks are associated with virtually all of these attempts.
One such attempt at managing two-stroke engine exhaust emissions has focused on improving the performance characteristics of small four-stroke engines in an attempt to adapt these four-stroke engines for at least some of the typical two-stroke engine applications. In particular, attempts have been made to implement a multiple valve arrangement in small four-stroke engines, such as has been done with four-stroke engines used in transportation applications. While arguably improving performance to some degree, such arrangements have increased the complexity of the modified four-stroke engines and have done little or nothing to reduce their weight. Thus, the relatively high PWR that is characteristic of two-stroke engines has not been preserved in these modified four stroke engines. As discussed earlier, a high PWR is critical for high performance lightweight vehicles such as snowmobiles, motor strokes, mopeds, lawn trimmers, lawn mowers, and the like.
Still other attempts to reduce and/or control emissions from two-stroke engines have been directed towards modifications of the process and devices used to introduce fuel into the cylinder. One such approach is commonly known as direct fuel injection (DFI). In contrast with more conventional two-stroke engines, a DFI two-stroke engine directly and independently directs fuel into the cylinder, rather than using the crankcase as a scavenging pump to draw oil and fuel from the carburetor to the cylinder. When properly designed and implemented, DFI systems have proven to be somewhat successful in reducing the emissions of two-stroke engines.
Any success achieved with DFI engines has come with significant attendant costs however. For example, the fuel injection components, such as the fuel pump, fuel injectors, sensors and electronic controls, add significantly to the manufacturing cost and thus the end cost of a two-stroke engine so modified. Additionally, the additional parts introduce a significant measure of mechanical complexity to the two-stroke engine. Because of the aforementioned additional complexity and cost, two-stroke engines utilizing DFI technology are not well suited to satisfy the ongoing demand for an inexpensive engine with a high PWR.
Other attempts to reduce and/or minimize heavy hydrocarbon emissions from two-stroke engines have focused on various reformulations of the fuel typically utilized by those engines. Generally, most of the alternative fuels comprise either ethanol or ethanol-gasoline blends in various proportions. One benefit of such fuel blends is that the discharge of aromatic hydrocarbons is significantly reduced. Unfortunately, there is a tradeoff associated with such a reduction. In particular, such fuel blends typically combust to produce an exhaust characterized by a relatively high amount of formaldehyde. Formaldehyde is a pollutant and its toxic effects, on aquatic environments in particular, are well known. Thus, it is a characteristic of these alternative fuel blends that a tradeoff is produced between emitting one type of pollutant versus another type of pollutant. Even if alternative fuel blends proved viable, it is likely that they would be of only limited availability in remote areas. This is a critical shortcoming in view of the environments in which two stroke engines are often employed, e.g., backcountry forests (as in the case of snowmobiles), remote lakes and remote ocean locations (as in the case of watercraft), and developing countries. In view of the foregoing, it appears that alternative fuel blends are not, at the present time, a highly viable solution to the emission problems characteristic of two-stroke engines.
At least one other attempt to manage exhaust emissions from two-stroke engines has focused on catalytic converter technology. Generally, a catalytic converter operates as an afterburner, burning hydrocarbon exhaust within the converter so that the exhaust is converted to carbon dioxide, carbon monoxide and water. However, catalytic converters are not well suited for use with two-stroke engines because they are prone to fouling and running hot under the high hydrocarbon loads that are characteristic of two-stroke engine operating conditions. Furthermore, catalytic converters have a finite life span and therefore several different converters may be consumed during the lifetime of an engine, thereby increasing the operational costs associated with the engine. Finally, because catalytic converters typically use precious metals to effectuate the conversion process, the converters tend to be relatively expensive.
The present invention has been developed in response to the current state of the art, and in particular, in response to these and other problems and needs that have not been fully or completely solved by currently available two-stroke engine exhaust systems. Thus, it is an overall object of the present invention to effectively resolve at least the problems and shortcomings identified herein. In particular, it is an object of the present invention to provide an exhaust system that materially reduces the emissions of heavy hydrocarbons by two-stroke engines without materially compromising the performance of the engine. It is also an object of the present invention to provide an exhaust system that is mechanically simple and can be readily retro-fitted to existing two-stroke engines. Finally, it is an object of the present invention to provide an exhaust system that is relatively light in weight and inexpensive.
In summary, the foregoing and other objects, advantages and features are achieved with an improved exhaust system for use in materially reducing heavy hydrocarbon emissions from internal combustion engines. Embodiments of the present invention are particularly suitable for use with two-stroke engines and the like.
In one embodiment, the improved exhaust system includes a vortex tube having a chamber in communication with the exhaust manifold of a two-stroke engine. The vortex tube includes an exhaust inlet connection and two gas outlet connections preferably in communication with the atmosphere. The opening of at least one of the gas outlet connections is adjustable so that the volume of gas exiting the vortex tube through that gas outlet connection may be varied as required to suit a particular application. The vortex tube further includes a liquid outlet connection to facilitate removal of separated liquids from the chamber. In one embodiment, the liquid connection of the vortex tube is in communication with the fuel intake line of the two-stroke engine. Finally, the vortex tube includes a nozzle assembly so arranged that exhaust entering the chamber by way of the exhaust inlet connection must first pass through the nozzle. The nozzle assembly preferably includes a nozzle having at least one inlet aperture tangentially oriented with respect to the diameter of the nozzle. Preferably, the inlet aperture has an available inlet area that varies in response to changes in the pressure of the exhaust. In a preferred embodiment, the available inlet area is varied by way of a resilient member, such as a spring, which is so arranged as to cause a blockage of a predetermined portion of the inlet aperture and thereby define the available inlet area, wherein the extent of the blockage corresponds to the pressure of the exhaust stream. By thus effectuating definition of the available inlet area, the resilient member facilitates control of the flow of exhaust through the nozzle.
In operation, an exhaust stream from the two-stroke engine initially enters the nozzle through the exhaust inlet connection. The tangentially arranged inlet apertures of the nozzle serve to impart a high velocity cyclonic, or rotational, motion to the exhaust stream so that the exhaust stream rotates as it passes down the vortex tube. Because of the high velocity of the cyclonic flow, the heavier liquid components of the exhaust stream are thrown to the periphery of the chamber defined by the vortex tube where they can be drawn off through the liquid connection. Preferably, at least a portion of the liquid components so separated are routed back to the cylinder for burning.
The remaining gaseous components of the exhaust stream exit the vortex tube through the gas outlet connections. In a preferred embodiment, a relatively cooler gaseous component exits the vortex tube through one of the gas outlet connections, and a relatively warmer gaseous component exits the vortex tube through the other gas outlet connection.
The present invention thus has among its various desirable features, the ability to separate out from gaseous components of the exhaust, relatively heavier components such as unburned fuel, oil, and/or other heavy hydrocarbons, which can then be routed back to the cylinder for burning. Consequently, emission of unburned heavy hydrocarbons by the two-stroke engine is substantially reduced, and fuel efficiency is improved since a much greater percentage of the fuel provided to the engine is burned. Further, because the nozzle through which exhaust is introduced to the vortex tube has an inlet aperture whose available inlet area is responsive to changes in the pressure of the exhaust stream produced by the two-stroke engine, the exhaust system is able to effectuate a high level of separation of liquid components of the exhaust stream even under varying exhaust stream pressures.
These and other objects, features, and advantages of the present invention will become more fully apparent from the following description and appended claims, or may be learned by the practice of the invention as set forth hereinafter.